A diurnal type scale. Construction, consistency and validation in shift work.
The purpose of the present study was (i) to construct a short scale with high internal reliability for use as a measure of "diurnal type" (morning or evening disposition), (ii) to validate the constructed index against sleep/wake behavior in connection with different workhours, (iii) to study inter- and intraindividual consistency over a 1-a interval, and (iv) to examine the effects of changed workhours on diurnal type scores. Three hundred shift workers filled out the same questionnaire twice with a 1-a interval. An index of seven items was constructed yielding a Cronbach alpha coefficient of 0.75. The analysis showed that the morning active (MA) individuals rose earlier and went to bed earlier than the evening active (EA) individuals, and the former had a longer sleep length than the latter during days with a morning shift, while the opposite was true for afternoon and night shifts. During days with a morning shift more EA individuals took naps, but during days with a night shift the MA group took naps more often than the EA group. The MA individuals had fewer sleep complaints than the EA individuals during the morning shift. The correlation was high (r - 0.79, p less than 0.001) for the index between the two administrations with a 1-a interval in between. Those who had changed from shift work to day work tended to report a more pronounced morning active disposition. However the interindividual consistency was still pronounced. It was concluded that the analysis resulted in a short diurnal type scale with high internal reliability and high consistency between measurements and that it differentiated between morning and evening types in sleep/wake habits.